G&P AR-15 guns (anything M4 or M16) are incredibly good, best externals for AR-15 AEG's and very good internals. The only thing you may have to upgrade is the hop rubber as the G&P hop rubbers can be a bit naff. But that is an extra £5 for a TM rubber and 100% skirmishable even without it, just maybe a little lacking on the range.